1. Field of the Invention
The invention relates to a rod-type flame glow plug for preheating the intake air of an internal combust ion engine, especially a diesel engine. More specifically, the present invention relates to a rod-type flame glow plug having a glow tube with an inn er p ole, a coil combination of at least one control and glow coil located in series in the glow tube with an ignition coil, the ignition coil being located at the tip of glow tube and making contact with the glow tube.
2. Description of Related Art
Rod-type flame glow plugs of the type to which the invention is directed are known, for example, from German Patent 43 01 252 and corresponding U.S. Pat. No. 5,468,993. The disadvantage of these rod-type flame glow plugs is the difficulty of arranging the coils exactly concentrically in the glow tube so that the distance from the outside edges of the coils to the inside edge of the glow tube is the same; this, in turn, is the prerequisite for heating taking place uniformly so that carbonization does not occur in the vaporizer area due to nonuniform heat formation on the adjacent glow tube wall. In addition, short circuits can occur which are caused by coil areas touching the glow tube. Short circuits can, likewise, be caused by destruction of conventional heating rod seals in the entry area of the inner pole into the glow tube of the plug.
The danger of nonconcentric arrangement of the coil(s) is especially problematic in the area of the glow tube tip at which the end of the glow coil is welded to the glow tube; but can also easily occur when the glow tube into which the coil or coil combination is inserted is filled with insulating material, such as MgO or AlN, for example, because the coils, and especially the 24 volt coils, are easily moved, especially in the control coil area, accordingly the fuel preheating and vaporizer area; however, bending of the coils can also occur during the conventional process of caulking the coil end in the inner pole connection. Here, it should be mentioned that 24 volt coils, as compared to 12 volt coils, have a much thinner cross section; this leads to a very soft spring rate of the 24 volt coils. Thus, 12 V/24 V control coils have diameters of roughly 0.6/0.35 mm and 12 V/24 V heating coils roughly 1.00/0.55 mm.
Finally, lack of roundness occurs with the same aforementioned disadvantages in the production of the coil combinations; this applies especially in the so-called 24 volt coils. The proportion of coils which are bent by careless transport is also not inconsiderable.